Don’t Throw Away That Old Calendar

mexico_2015_calendarThat old 2015 calendar?  You can re-use it in 2026!  You will have to wait until 2044 to re-use your 2016 calendar.  But you can re-use a 2017 calendar in 2017 calendar in 2023.  (Of course, there’s a When can I reuse this calendar? website.)

If you save a calendar every year, eventually you won’t have to buy any. Often you can re-use a calendar for a given year 11 years later, though sometimes it’s only 6 years later, and sometimes it’s 12, or it could be more.

Why can calendars be re-used?  Because there are only 14 different calendars.

There would only be 7 different calendars, like this:

  • the first day of the year is a Sunday,
  • or a Monday,
  • or a Tuesday,

except for the extra day on February 29 that usually occurs once every 4 years. Given the more-or-less quadrennial extra day, there are actually 14 different calendars:

  • the year starts on a Sunday and doesn’t have an extra day,
  • the year starts on a Sunday and has an extra day,
  • the year starts on a Monday and doesn’t have an extra day,
  • the year starts on a Monday and has an extra day

Once you collect all 14, you’re ready to stop buying calendars!

For more information:

http://fivethirtyeight.com/features/riddler-how-long-before-you-can-use-your-2015-calendar-again-riddler/
& (the answer)
http://fivethirtyeight.com/features/how-badly-can-a-car-salesman-swindle-you/

http://whencanireusethiscalendar.com/

http://www.hermetic.ch/cal_sw/idcal/idcal.htm

 

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